Sonochemical synthesis of highly monodispersed and size controllable Ag nanoparticles in ethanol solution

Highly monodispersed Ag nanoparticles (NPs) were prepared by a sonochemical method, in which Ag⁺ in an ethanol solution of AgNO₃ was reduced by ultrasound irradiation in the presence of benzyl mercaptan without the additional step of introducing other reducing reagents or protective reagents. In addition to the stabilizing effect, benzyl mercaptan remarkably enhanced the reduction rate, probably due to the thermal decomposition that occurs at the interfacial region between cavitation bubbles and bulk solution and provides reducing radicals. More importantly, the size of Ag NPs can be controlled by simply tuning the initial molar ratio of benzyl mercaptan to Ag, which was confirmed by transmission electron microscopy and ultraviolet-visible absorption spectrometry, as well as X-ray diffraction.     

Black tea leaf extract derived Ag nanoparticle-PVA composite film: Structural and dielectric properties

Biosynthesized metal (Ag) nanoparticles have been used to prepare high dielectric polymer composite film of technological importance. Different amounts of the tea leaf extract (E) (mother leaker prepared by soaking 2 g tea leaf in 100 ml boiled water for 3 min) were used to synthesize silver nanoparticles from 10⁻³ M AgNO₃ solution. Such a resultant solution containing Ag nanoparticles was mixed with 20 ml PVA solution (5 g PVA in 100 ml water) was used to make anhydrous Ag/PVA composite film where spherical silver nanoparticles (AgNPs) of average diameter 10 nm are well dispersed in the composite. The Ag particle size in the composite was found to enhance with the increase of E content in PVA. XRD, SEM, TEM, FT-IR, UV–vis, TGA and DSC studies are made to characterize the nanoparticles. Detailed frequency and E concentration dependent electrical and dielectric properties of the nanocomposites have been made showing low loss (∼0.14) and high dielectric property of these films. Maximum value of dielectric permittivity (∼900 which is almost 170 times higher than that of pure PVA ∼ 5.2) have been observed for 15 ml E-AgNPs/PVA nanocomposite film at 1 kHz and room temperature. Present study establishes the importance of the biosynthesized metal nanoparticles for industrial applications as in capacitors.     

Facile synthesis of Ag nanoparticles supported on TiO2 inverse opal with enhanced visible-light photocatalytic activity

TiO₂ inverse opal films loaded with silver nanoparticles (ATIO) were synthesized on glass substrates. TiO₂ inverse opal (TIO) films were prepared via a sol-gel process using self-assembly of SiO₂ colloidal crystal template and a facile wet chemical route featuring an AgNO₃ precursor solution to fabricate silver nanoparticles on the TIO films. The inverse opal structure and Ag deposition physically and chemically modify titania, respectively. The catalysts were characterized by Raman spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), UV-vis absorption spectra, X-ray photoelectron spectroscopy and photoluminescence spectroscopy. The HRTEM results show that Ag nanoparticles measuring 5-10 nm were evenly distributed on TIO. Both the UV- and visible-light photocatalytic activities of the samples were evaluated by analyzing the degradation of methylene blue (MB) in aqueous solution. The results reveal that the apparent reaction rate constant (k_app) of MB degradation of the sample ATIO under UV-light irradiation is approximately 1.5 times that of the conventional Ag-loaded TiO₂ film (ATF) without an ordered porous structure at an AgNO₃ concentration of 5 mM in the precursor solution. At an AgNO₃ concentration of 10 mM, the sample exhibits a k_app value approximately 4.2 times that of ATF under visible-light irradiation. This enhanced visible-light photocatalytic performance can be attributed to the synergistic effect of optimized Ag nanoparticle deposition and an ordered macroporous TIO structure. Repeated cycling tests revealed that the samples showed stable photocatalytic activity, even after six repeated cycles.     

Characterization of silica-coated Ag nanoparticles synthesized using a water-soluble nanoparticle micelle

This article describes the synthesis of silica-coated Ag nanoparticles using a water-soluble nanoparticle micelle under basic conditions. Monodispersed Ag nanoparticles with a mean particle size of 7 nm were synthesized using AgNO₃ in the presence of ascorbic acid as a reducing agent. The Ag nanoparticles were easily re-dispersed into an aqueous solution by surface adsorption of surfactant molecules, indicating formation of water-soluble nanoparticle micelles. Silica-coated Ag nanoparticles ranging in size from 50 to 100 nm were obtained by controlling the surfactant, Ag nanoparticle and tetraethylortho silicate (TEOS) concentrations. Adsorbed surfactant monolayers on Ag nanoparticles were used as a template for the silica shell because of the hydrophobicity of TEOS. In all cases, the size of the resulting particles increased linearly as these concentrations increased. Based on transmission electron microscopy, all the Ag nanoparticles were completely covered with a silica shell. In most samples, however, Ag nanoparticle size increased from 7 to 50 nm due to evaporation of hexane by heating. Although mean particle size of silica-coated Ag nanoparticles was drastically altered, characteristic absorption peaks were observed at approximately 410 nm.     

Hydroxy propyl cellulose capped silver nanoparticles produced by simple dialysis process

Silver (Ag) nanoparticles (∼6 nm) were synthesized using a novel dialysis process. Silver nitrate was used as a starting precursor, ethylene glycol as solvent and hydroxy propyl cellulose (HPC) introduced as a capping agent. Different batches of reaction mixtures were prepared with different concentrations of silver nitrate (AgNO₃). After the reduction and aging, these solutions were subjected to ultra-violet visible spectroscopy (UVS). Optimized solution, containing 250 mg AgNO₃ revealed strong plasmon resonance peak at ∼410 nm in the spectrum indicating good colloidal state of Ag nanoparticles in the diluted solution. The optimized solution was subjected to dialysis process to remove any unreacted solvent. UVS of the optimized solution after dialysis showed the plasmon resonance peak shifting to ∼440 nm indicating the reduction of Ag ions into zero-valent Ag. This solution was dried at 80 °C and the resultant HPC capped Ag (HPC/Ag) nanoparticles were studied using transmission electron microscopy (TEM) for their particle size and morphology. The particle size distribution (PSD) analysis of these nanoparticles showed skewed distribution plot with particle size ranging from 3 to 18 nm. The nanoparticles were characterized for phase composition using X-ray diffractrometry (XRD) and Fourier transform infrared spectroscopy (FT-IR).     

Synthesis of Ag modified vanadium oxide nanotubes and their antibacterial properties

Vanadium oxide nanotubes (VO_x-NTs) modified by highly dispersed Ag nanoparticles have been synthesized via a facile silver-mirror reaction. The crucial factors that affected the preparation of the Ag modified vanadium oxide nanotubes (Ag/VO_x-NTs) have been also studied. The dispersion and structure of Ag nanoparticles in the obtained materials were characterized by transmission electron microscopy (TEM), electron diffraction (ED) and X-ray diffraction (XRD). The results showed the distribution and size of the formed Ag particles were greatly influenced by the concentration of AgNO₃ solution. Typically, Ag nanoparticles were well dispersed on the VO_x-NTs with the size range from 3 to 10 nm. The corresponding antibacterial tests demonstrated the as-synthesized Ag/VO_x-NTs exhibited strong antibacterial activity against Escherichia coli (E. coli).     

Synthesis of polypyrrole nanocomposites decorated with silver nanoparticles with electrocatalysis and antibacterial property

Polypyrrole nanowire/silver nanoparticle composites (PPy/Ag) are obtained in aqueous media through a one-pot method without any external stimulus. PPy nanowires were assembled on the reactive self-degraded template of the complex of AgNO₃ and methyl orange (MO). During the synthesis process in the dark surrounding, Ag nanoparticles could be uniformly decorated onto the surface of PPy nanowires in situ by the redox reaction of pyrrole and AgNO₃. Neither additional reducing agents for the growth of silver nanoparticles nor oxidizing agents for the polymerization of pyrrole are utilized. The formation mechanism, morphologies, structural characteristics, and conductivity of the obtained PPy/Ag nanocomposites are reported. The as-prepared PPy/Ag nanocomposites exhibit well-defined response to the electrochemical reduction of hydrogen peroxide. Moreover, the preliminary antibacterial assays indicate that the PPy/Ag nanocomposites also possess antibacterial abilities against Escherichia coli.     

Optimisation of nitrate reductase enzyme activity to synthesise silver nanoparticles

Today, the synthesis of silver nanoparticles (Ag NPs) is very common since it has many applications in different areas. The synthesis of these nanoparticles is done by means of physical, chemical, or biological methods. However, due to its inexpensive and environmentally friendly features, the biological method is more preferable. In the present study, using nitrate reductase enzyme available in the Escherichia coli (E. coli) bacterium, the biosynthesis of Ag NPs was investigated. In addition, the activity of the nitrate reductase enzyme was optimised by changing its cultural conditions, and the effects of silver nitrate (AgNO₃) concentration and enzyme amount on nanoparticles synthesis were studied. Finally, the produced nanoparticles were studied using ultraviolet –visible (UV–Vis) spectrophotometer, dynamic light scattering technique, and transmission electron microscopy. UV–Visible spectrophotometric study showed the characteristic peak for Ag NPs at wavelength 405–420 nm for 1 mM metal precursor solution (AgNO₃) with 1, 5, 10, and 20 cc supernatant and 435 nm for 0.01M AgNO₃ with 20 cc supernatant. In this study, it was found that there is a direct relationship between the AgNO₃ concentration and the size of produced Ag NPs.Inspec keywords: enzymes, molecular biophysics, silver, nanoparticles, nanofabrication, microorganisms, cellular biophysics, silver compounds, ultraviolet spectra, visible spectra, light scattering, transmission electron microscopyOther keywords: nitrate reductase enzyme activity, optimisation, silver nanoparticle synthesis, Escherichia coli bacterium, E. coli bacterium, biosynthesis, ultraviolet‐visible spectrophotometer, UV‐vis spectrophotometer, dynamic light scattering technique, transmission electron microscopy, supernatant, metal precursor solution, AgNO₃ ‐Ag     

Biosynthesis of AgNPs by B. maydis and its antifungal effect against Exserohilum turcicum

In the present study, Bipolaris maydis was used to synthesise silver nanoparticles (AgNPs). Several parameters that influence the synthesis of AgNPs such as fungus age, the concentration of Ag nitrate (AgNO₃), and incubation time were explored to find the optimum synthesis condition. Furthermore, the antifungal activity of AgNPs against Exserohilum turcicum was determined by measuring inhibition zone diameter, colony formation, and conidia germination. The optimal biosynthesis system included fungus age of 7 days, 8 mM AgNO₃, and an incubation time of 120 h. Under these conditions, synthesised NPs were near round, and the average particle size was about 21 nm. At the experiment, the diameter of the inhibition zone reached a maximum of 8 mM AgNO₃ and 72 h. In addition, the inhibition rate of colony and conidia reached 83.39 and 100%, respectively, with 200 μg/ml AgNPs. The results offer a novel pathway for phytopathogen control and make it likely to develop new eco‐friendly antimicrobial.Inspec keywords: silver, nanoparticles, antibacterial activity, microorganisms, particle size, nanomedicine, nanofabricationOther keywords: biosynthesis, B. maydis, antifungal effect, Exserohilum turcicum, Bipolaris maydis, silver nanoparticles, fungus age, silver nitrate concentration, incubation time, inhibition zone diameter, colony formation, conidia germination, particle size, phytopathogen control, time 72 h, time 120 h, Ag     

Ag nanoclusters synthesized by successive ionic layer deposition method and their characterization

The possibilities of successive ionic layer deposition technology for synthesizing the Ag nanoclusters and nanolayers were analyzed in present article. It was shown that this technology, based on successive treatments of appropriate substrates in solution of cations and anions, is acceptable for the controllable forming of the Ag nanoparticles at the surface of different substrates. Results related to characterization of the Ag nanoclusters synthesized using Ag(NH₃)₂NO₃ or AgNO₃ precursors were discussed. It was found that the concentration and the size of the Ag nanoparticles deposited on a surface of fused quartz, silica gel, and monocrystalline silicon can be controlled by varying composition and pH of the reagent solutions as well as the number of the deposition cycles. It was established that the size of Ag nanoclusters depending on a synthesis conditions may vary from 1–5 nm to 500 nm. Model explained the growth of Ag clusters during successive ionic layer deposition was discussed as well.     

Fabrication of Ag nanoparticles dispersed in PVA nanowire mats by microwave irradiation and electro-spinning

In this study, the antimicrobial substance, silver nanoparticles (Ag NPs) loaded in poly (vinyl alcohol) (PVA) nanowire mats were fabricated by conjugation of the electro-spinning method and the microwave-assisted process. The best PVA nanowire mats were fabricated by through control of electro-spinning conditions, which were applied for fabrication of Ag NPs loaded in PVA nanowires. PVA was used not only as a carrier for loading of Ag NPs but also as a reduction agent with which the Ag⁺ ion was already reduced to a large number of Ag NPs by irradiation with a microwave. Ag NPs were synthesized inside the PVA solution depending on the time of microwave irradiation — whether for 60 s or 90 s. Size distribution of Ag NPs was 5–10 nm in diameter for 60 s; and 10–20 nm in diameter for 90 s of irradiation. Presence of Ag NPs acquired through microwave assisted irradiation was confirmed by X-ray diffraction profiles (XRD). Microstructure, particle size distribution, and morphology of both the nanowire mats and the Ag particles were investigated using SEM and TEM techniques. The effect of Ag-NPs on the PVA mechanical property of nano-fibrous mats was investigated according to tensile strength. Antibacterial activity of PVA loaded Ag NPs at different irradiation times was tested on Gram-positive bacteria, Staphylococcus aureus Gram-negative bacteria, and Escherichia coli.     

Synthesis of high tap density spherical micro-size silver particles by liquid-phase reduction using response surface methodology

Mono-disperse and spherical micro-size silver particles with high tap density were prepared by using silver nitrate as metal source, ascorbic acid as reductant, sulfuric acid as dispersant and polyethylene glycol 4000 (PEG4000) as surfactant. The aim of this paper was to study the simultaneous effects of surfactant dosage (PEG4000/AgNO₃ mass ratio), silver nitrate concentration [AgNO₃], deionized water dosage in reductant solution, stirring rate and their interactions on properties of silver particles. For optimizing these parameters, irregular fractional factorial design of experiments was used. As-prepared silver particles were characterized by X-ray diffraction, scanning electron microscopy, laser particle size analyzer and tap density (tap density refers to the stacking density of particles after vibration compaction) meter. The results showed that silver particles were spherical, mono-disperse and with high tap density (>5.0 g/mL), average particle size of about 2–3 μm and narrow particle size distribution. By surveying the experiment results and analysis of variance, two mathematical models were obtained and optimized parameters were determined. Analysis of the variance demonstrated that the interaction of [AgNO₃] and stirring rate were the most significant factor affecting particle size and PEG4000/AgNO₃ mass ratio and [AgNO₃] were main significant factors affecting tap density. The predicted particle size and tap density were respectively 2.5 μm and 5.065 g/mL while the experimental results were 2.52 μm and 5.108 g/mL, which indicated that the models were in good agreement with the experimental data.     

Preparation and size control of silver nanoparticles by a thermal method

In this letter we report that stable silver nanoparticles can be facilely prepared directly from an amine-containing polyelectrolyte/AgNO₃ aqueous solution without the additional step of introducing other reducing agents and protective agents through a thermal process. More importantly, the size of nanoparticles thus formed can be controlled by the initial molar ratio of polyelectrolyte to Ag.     

Controllable synthesis of fluorescent silver nanoparticles with different length oligonucleotides

Silver nanomaterials have become important research topics in recent years. As a new type of fluorescent material, silver nanomaterials have been applied to fluorescent sensors, bioimaging and materials targeting cancer cells. Here, an approach to the oligonucleotide‐templated controllable formation of fluorescent Ag nanomaterials is reported. In this experiment, silver nanoparticles (NPs) were synthesised from oligonucleotides chains, sodium borohydride (NaBH₄) and silver nitrate (AgNO₃) by changing the molar ratio of DNA to sodium borohydride (NaBH₄) and silver nitrate (AgNO₃). Fluorescent assay and transmission electron microscopy were used to characterise the silver NPs. The optimal selection of DNA chains with different lengths as templates for the synthesis of silver NPs was found. This work successfully develops the capping oligonucleotides scaffolds of silver nanoclusters.     

Silver, gold and bimetallic nanoparticles production using single-cell protein (Spirulina platensis) Geitler

Interaction of single-cell protein of Spirulina platensis with aqueous AgNO₃ and HAuCl₄ was investigated for the synthesis of Ag, Au and Au core—Ag shell nanoparticles. Biological reduction and extracellular synthesis of nanoparticles were achieved in 120 h at 37 °C at pH 5.6. The nanometallic dispersions were characterized by surface plasmon absorbance measuring at 424 and 530 nm for Ag and Au nanoparticles, respectively. For bimetallic nanoparticles, absorption peak was observed at 509, 486 and 464 nm at 75:25, 50:50 and 25:75 (Au:Ag) mol concentrations, respectively. High-resolution transmission electron microscopy showed formation of nanoparticles in the range of 7–16 (silver), 6–10 (gold) and 17–25 nm (bimetallic 50:50 ratio). XRD analysis of the silver and gold nanoparticles confirmed the formation of metallic silver and gold. Fourier transform infrared spectroscopic measurements revealed the fact that the protein is the possible biomolecule responsible for the reduction and capping of the biosynthesized nanoparticles.     

Assembly, characterization and swelling kinetics of Ag nanoparticles in PDMAA-g-PVA hydrogel networks

A series of poly(N,N-dimethylacrylamide)-g-poly(vinyl alcohol) (PDMAA-g-PVA) graft hydrogel networks were designed and prepared via a free radical polymerization route initiated by a PVA-(NH₄)₂Ce(NO₃)₆ redox reaction. Silver nanoparticles with high stability and good distribution behavior have been self-assembled by using these hydrogel networks as a nanoreactor and in situ reducing system. Meanwhile the PDMAA or PVA chains can efficiently act as stabilizing agents for the Ag nanoparticles in that Ag⁺ would form complex via oxygen atom and nitrogen atom, and form weak coordination bonds, thus astricting Ag⁺. The structure of the PDMAA-g-PVA/Ag was characterized by a Fourier transform infrared spectroscope (FTIR). The morphologies of pure PDMAA-g-PVA hydrogels and PDMAA-g-PVA/Ag nanocomposite ones were observed by a scanning electron microscopy (SEM) and transmission electron microscope (TEM). TEM micrographs revealed the presence of nearly spherical and well-separated Ag nanoparticles with diameters ranging from 10 to 20 nm, depending on their reduction routes. XRD results showed all relevant Bragg's reflection for crystal structure of Ag nanoparticles. UV–vis studies apparently showed the characteristic surface plasmon band at 410–440 nm for the existence of Ag nanoparticles within the hydrogel matrix. The swelling kinetics demonstrated that the transport mechanism belongs to non-Fickian mode for the PDMAA-g-PVA hydrogels and PDMAA-g-PVA/Ag nanocomposite ones. With increasing the DMAA proportion, the r₀ and S_∞ are enhanced for each system. The assembly of Ag nanoparticles and the swelling behavior may be controlled and modulated by means of the compositional ratios of PVA to DMAA and reduction systems.     

Photoelectrochemical performance of Ag nanoparticles on TiO2 films prepared by aerosol pyrolysis

Titanium dioxide (TiO₂) layers were prepared by the pyrolysis of an ethanolic solution of di-iso-propoxy-titanium bis(acetylacetonate) in aerosol form, and then electrodeposited with Ag nanoparticles on their surface. The morphology and photoelectrochemical properties of the resulting Ag nanoparticles (NPs) on TiO₂ films were found to be significantly tuned by varying the electrodeposition time in an aqueous electrolyte containing AgNO₃ and KNO₃. Photocurrent density–voltage curves and electrochemical impedance spectra revealed that the Ag NPs remarkably improved the short-circuit current density and open circuit voltage, and considerably reduced the electrochemical impedance. Therefore, Ag NPs deposition enhanced the photo-absorption of the TiO₂ layer, excited photoelectrons by localised surface plasmon resonance, promoted photo-induced charge separation, and prevented electron–hole recombination.     

Preparation,characterisation and kinetics of corn-shaped Ag nanoparticles

Conventional UV-vis spectroscopic and transmission electron microscopy methods were used to monitor the kinetics, formation and characterisation of silver nanoparticles in the methionine-promoted reduction of silver(I). The silver nanoparticles (purple colour; λ _max?=?550?nm) are corn-shaped and aggregated, and the average particle size is about 23?nm. The kinetics of silver nanoparticles formation has been studied as a function of [Ag(I)], [methionine] and [CTAB]. We see that [Ag(I)] has no effect on the rate of silver nanoparticles formation. At higher [CTAB]?≥?40.0?×?10^?4?mol?dm^?3, silver nanoparticles were not observed. Methionine is responsible for interparticle interaction, increase in aggregate size and cross-linking between the particles, and it acts as complexing, reducing, adsorbing and capping agents. A mechanism consistent with the observed kinetics has been proposed and discussed.     

Gamma-irradiation-induced Ag/SiO2 composite films and their optical absorption properties

Small Ag particles or clusters dispersed mesoporous SiO₂ composite films were prepared by a new method: First the matrix SiO₂ films were prepared by sol-gel process combined with the dip-coating technique, then they were soaked in AgNO₃ solutions followed by irradiation of γ-ray at room temperature and in ambient pressure. The structures of these films were examined by X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), and optical absorption spectroscopy. It has been shown that the Ag particles grown within the porous SiO₂ films are very small, and they are isolated and dispersed from each other with very narrow size distributions. With increasing the soaking concentration and an additional annealing, an opposite peakshift effect of the surface plasmon resonance (SPR) was observed in the optical absorption measurements.